Significant resources have been and continue to be devoted to the development and public dissemination of reports comparing the performance of health plans. By requiring health plans participating in the Medicare+Choice program to provide standardized measures of performance, the Centers for Medicaid and Medicare Services (CMS) has been a leader in promoting these efforts. Although the objective of health plan performance measurement and reporting is to improve the quality of healthcare by providing consumers with the information necessary to incorporate quality into their health care purchasing decisions and providers with information on how their performance compares with others, evidence supporting the effectiveness of these interventions is lacking. The objective of this research is examine the effect of health plan participation in quality measurement and reporting on the use of measured services by Medicare beneficiaries. Our research will have two specific aims: (1) To determine how the implementation of mandatory health plan participation in standardized quality measurement and performance affected the utilization of measured services among Medicare beneficiaries enrolled in these plans; and (2) To determine whether mandated performance measurement and reporting affected the utilization of measured services by beneficiaries enrolled in traditional Medicare. We will achieve the first objective by examining the utilization of measured services among elderly Medicare beneficiaries enrolled in Medicare+Choice plans before and after the implementation of mandated participation in HEDIS performance measurement and reporting and comparing changes among these beneficiaries to those enrolled in traditional Medicare. We will achieve the second objective by examining the effect of market level enrollment in Medicare+Choice on utilization of measured services among individuals enrolled in traditional Medicare before and after the implementation of mandatory quality reporting. The primary data source for our analyses will be the Medicare Current Beneficiary Survey. If we achieve these objectives, we will have provided information which is crucial for evaluating the effectiveness of consumer report cards in improving quality of care. This information is essential for both large purchasers, such as the Medicare program and employers, and policy makers to determine the appropriate role of these types of interventions in improving quality of care.